The present invention relates to the technical field of spliced bill detection and discloses a detection method for a spliced bill and a detection device for a spliced bill. According to the detection method, a transverse Sobel operator and a longitudinal Sobel operator are used to carry out edge detection and enhancement processing on a regional image to be detected so as to obtain a first image and a second image, the first image and the second image are subjected to projection processing so as to obtain a transverse gray level projection curve and a longitudinal gray level projection curve, through judging whether the projection results of the transverse gray level projection curve and the longitudinal gray level projection curve are in accordance with requirements of a normal bill so as to identify whether a bill is a spliced bill. Since the spliced bill can be accurately detected by the detection method of the spliced bill and the binarization processing and Hough transformation processing of a bill image are needed, the detection complexity of the spliced bill is reduced, and thus the detection efficiency of the spliced bill is improved.